Systems such as those shown in Morchand U.S. Pat. Nos. 3,180,931 and 3,256,386 have been provided for simultaneously transmitting over a single television channel carrier frequency a plurality of pictures or scenes which are normally displayed in the four quadrants of a television receiving tube. In these systems, one or more of the quadrants can be blanked out by switches at the receiver so that the viewer sees only a selected one or more of the quadrants.
An arrangement of this sort is particularly adaptable for use in educational television systems. Thus, the instructor at a transmitting station may cause different scenes or written material to appear at the four quadrants of a remote receiving tube as viewed by a student. He could then pose a problem via the audio channel of the television system and ask which one of the four quadrants contains the correct answer (i.e., a multiple choice question). By depressing one of four switches at the receiver, the student would then blank out all but one of the four quadrants which he feels contains the correct answer. The instructor would then advise students viewing individual receiving tubes of the correct answer.
Let us assume, for example, that the correct answer is in the fourth quadrant of the picture tube. If the student picked the wrong answer, he would be instructed to depress the switch for the correct quadrant; whereupon the subject matter shown in the correct quadrant would be discussed by the instructor.
Such systems, while usable, are not altogether satisfactory for the reason that the information ultimately studied by the students will be in only one quadrant and one corner of the television picture tube and, of course, one-quarter the size of the tube. As a result, the viewer may have difficulty in reading written material or even in viewing a scene.